Final answer:
The term for a pair of alleles being identical due to shared ancestry is homozygous. A homozygous organism has two identical alleles for a gene, either as homozygous dominant or homozygous recessive, which affects its genotype and potentially its phenotype.
Step-by-step explanation:
The term for a pair of alleles (or gene copies) being identical because of shared ancestry is homozygous. Alleles are different versions of genes, and in diploid organisms, two homologous chromosomes may carry identical alleles of a gene, making the organism homozygous for that trait. This is in contrast to heterozygous, where an organism has two different alleles of a gene on their two homologous chromosomes.
An organism can be homozygous dominant (AA) or homozygous recessive (aa) depending on the alleles it possesses. The genotype is the organism's genetic makeup, while the phenotype is the observable traits. Even though homozygous dominant and heterozygous organisms may look identical due to the dominant allele's effect on the phenotype, their genotypes are different because the heterozygous organism carries one dominant and one recessive allele (Aa).